87 JOURNAL OF THE 
found in the Peromeduse and the Ephyropside (Vausz- 
thoé), and is merely analogous to, not homologous with, 
the velum of the Hydromeduse. That this is the case 
is borne out by tke presence in the velum of gastrovascu- 
lar diverticula. This resemblance to the Hydromeduse 
is regarded by most naturalists as one of the numerous 
cases of convergent evolution exhibited by the twogroups 
of jelly-fish (Hydro- and Scyphomedusz), due to similari- 
ty in environment and toa certain similarity in the an- 
cestral polyps from which the two groups have been de- 
rived. 
The Cubomeduse are so rare that in spite of their in- 
teresting features, interesting alike to the student of 
phylogeny and nerve-physiology, few naturalists have 
had the opportunity of studying them. Our knowledge 
of the group has rested mainly on Claus’s description of 
Charybdea marsupialis (Wien. Arb. 1878). This very 
valuable paper, as Conant remarks, is written ina style 
difficult of comprehension, and many students who read 
with pleasure and profit the lucid treatises on medusan 
structure by the Hertwigsand Haeckel have turned away 
discouraged from Claus’s work. To Claus’s account, 
Haeckel in his ‘‘System”’ has added but little. The only 
other investigator of the group is Schewiakoff (1889), 
who has studied the remarkable sense organs. 
Through Conant’s discovery in 1896 of two new species 
(Charybdea Xaymacana and Tripedalia cystophora), 
which are present in abundance in Jamaican waters, the 
Marine Laboratory of the Johns Hopkins University has 
once again made accessible to students, material for the 
pursuit of investigations of wide interest. It was for the 
purpose of continuing his study of this group that Conant, 
in the summer of 1897, revisited Jamaica, and, as we 
learn from Professor Brooks’s introduction, he succeeded 
in making many observations on the physiology of the 
SS ws 
